Hbiss is on the right track.
It's not simply a matter of applying NEC tables, and other rules, to datacom wire. The NEC was never intended for such applications.
For example, typical Cat 5 specs limit your pulling force to 25 lbs ... total. It matters not how many cables are being pulled, 25 lbs is the limit.
Another insight may be obtained from phone co. specs for their lines. They'll want a 4" pipe, with a maximum of 2-90's in bends, for a single 25 pair line. (A 25 pair line is something like 5/8" OD).
Finally, I recently pulled a single 3-pair cat 3 cable through a 1/2" PVC pipe to a detached garage. While the pipe seemed plenty large, the pull was harder than I expected. It's the last time I'll make that mistake .... I think I'll START with 1" for any but the shortest cable drops.
